There are millions of different substances in the world. Some, like water, occur naturally. Others, like paper and plastic, are made in factories. Some substances, like sugar and blood, are made by living things. All substances have one important thing in common: they are all made of the tiny building blocks of matter that we call atoms. 7 Elements, compounds and mixtures Think about substances • How did plumbers get their name? • Which metal can drive you crazy? • Can water be split? • Can you breathe nitrogen gas? • What is most of an atom made up of? • Just what is ‘plastic’ made from? • Which precious gem is made from the same substance as charcoal and soot? In this chapter: 7.1 SCIENCE AS A HUMAN ENDEAVOUR It’s elementary 228 7.2 Elements: The inside story 230 7.3 Compounding the situation 233 7.4 Grouping elements 236 7.5 Patterns, order and organisation: Chemical name tags 238 7.6 Making molecules 240 7.7 Carbon: It’s everywhere 242 7.8 Thinking tools: Affinity diagrams and cluster maps Study checklist/Digital resources 244 Looking back 245 ICT ACTIVITY Science TV 247 ONLINE PAGE PROOFS
Transcript
There are millions of different substances in the world. Some, like water, occur naturally. Others, like paper and plastic, are made in factories. Some substances, like sugar and blood, are made by living things. All substances have one important thing in common: they are all made of the tiny building blocks of matter that we call atoms.
7 Elements, compounds and mixtures
Think about substances• Howdidplumbersgettheirname?• Whichmetalcandriveyoucrazy?• Canwaterbesplit?• Canyoubreathenitrogengas?• Whatismostofanatommadeupof?• Justwhatis‘plastic’madefrom?• Whichpreciousgemismadefromthe
What’s inside?How do you know what’s inside a substance when you can’t actually see inside it and it is so small that you can’t see it even with the most powerful microscope? It seems impossible — but it can be done!
INVESTIGATION 7.2
AIM To experience the difficulties of describing an object that cannot be seen
About 1000 years ago, when kings and queens lived in castles and were defended by knights in shining armour, there lived the alchemists.
7.1 S C I E N C E A S A H U M A N E N D E A V O U R
It’s elementary Lavoisier and hydrogenWatch a video from The story of science about the discovery of the elements.
eles-1772
eLesson
HOW ABOUT THAT!
Lewis Carroll’s Mad Hatter character in Alice’s Adventures in Wonderland was mad because mercury was used in the making of hats.
They chanted secret spells while they mixed magic potions in their flasks and melted metals in their furnaces. They tried to change ordinary metals into gold. They also tried to find a potion that would make humans live forever. They studied the movements of the stars and claimed to be able to see into the future. Kings and queens took the advice of the alchemists very seriously.
The alchemists never found the secrets they were looking for, but they did discover many things about substances around us. During the same period people who worked with materials also helped us to understand many everyday substances. Blacksmiths worked with metals to make stronger and lighter swords and armour, fabric dyers learned how to colour cloth, and potters decorated their work with glazes from the Earth. Without the
knowledge passed down by these people, the world as we know it would be very different! Twelve important substances were discovered during these
ancient times: gold, iron, silver, sulfur, carbon, lead, mercury,
tin, arsenic, bismuth, antimony and copper. Alchemists discovered
five of these.
Real scienceIn about the seventeenth century, people stopped thinking about magic and instead carried out
investigations based on careful observations. These new seekers of knowledge
were called scientists. They discovered that the 12 substances could not be broken down into other substances. Scientists investigated many common everyday substances as well, including salt, air,
rocks, water and even urine! They discovered that nearly
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everything around us could be broken down into other substances. They gave the name ‘element’ to the substances that could not be broken down into other substances. Between 1557 and 1925, another 76 elements were discovered. We now know that 92 elements exist naturally. In recent years scientists working in laboratories have been able to make at least another 24 artificial elements.
Warning! Danger!Many elements are safe to handle. However, there are also many that are not. For example, the elements
sodium, potassium and mercury need special care and handling. Sodium and potassium are soft metals that can be cut with a knife. They both get very hot if they come into contact with water. They are stored under oil so that water in the atmosphere cannot reach them.
Elements are rareMost of the substances around you are made up of two or more elements. You will not be able to find many of the 92 naturally occurring elements in their pure form. It is possible, however, to examine many of the elements in the school laboratory.
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INVESTIGATION 7.3
Checking out appearances AIM To examine and describe the properties of a selection of elements
METHOD AND RESULTS
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Elements State Description In which substances might the element be present?
Hydrogen Gas Clear, colourless, explosive Acids, water
7.1 How big is an atom?worksheet
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7.2
Elements: The inside storyAbout 2500 years ago a teacher named Democritus lived in ancient Greece. He walked around the gardens with his students, talking about all sorts of ideas.
Democritus suggested that everything in the world was made up of tiny particles so small that they couldn’t be seen. He called these particles atomos, which means ‘unable to be divided’. Other thinkers at the time disagreed with Democritus. It took about 2400 years for evidence of the existence of these atoms (as we now call them) to be found.
Atoms and elementsWe now know that each element is made of its own particular kind of atom. Gold contains only gold atoms, oxygen contains only oxygen atoms, carbon contains only carbon atoms and so on. But what is it that makes atoms different from one another? To answer this question we need to know a little bit more about the atom.
For scientists, the atom was like the mystery box on page 227. Even though the atom couldn’t be seen, scientists did experiments over many years and they thought carefully about the information they gathered.
Finding evidence for the existence of atoms was not possible until Galileo wrote about the need for controlled experiments and the importance of accurate observations and mathematical analysis in the 16th century. Galileo’s ‘scientific method’, along with the development of more accurate weighing machines, was used by John Dalton in 1803 to show that matter was made up of atoms. He proposed that atoms could not be divided into smaller particles and that atoms of different elements had different masses.
For the next 100 years, scientists thought the atom was a solid sphere, but discoveries including radioactivity and electric current, and new technology such as the vacuum tube and Geiger counters, allowed scientists to ‘peek’ inside.
Positive nucleus
Electron
Rutherford’s model of the atom
In 1911, New Zealander Sir Ernest Rutherford used some of the new discoveries and inventions to prove that atoms were not solid particles.
He fired extremely tiny particles at a very thin sheet of gold. Most of the particles went straight through. Only sometimes did they bounce off as if they had hit something solid. He concluded that the tiny particles could be getting through only if most of each atom consisted of empty space.
Niels Bohr proposed the next model of the atom. He suggested that the electrons changed their orbits around the positively charged nucleus and formed electron ‘clouds’.
Orbital electronsnegatively charged
Nucleus, containingpositively charged protons
Bohr’s model of the atom
The Chadwick–Bohr model
In 1932 James Chadwick found another type of particle in the nucleus of the atom — the neutron.
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The particles in thecentre of an atom are calledprotons and neutrons.Together they form thenucleus. Each protoncarries a positiveelectric charge. Neutronshave no electric charge.
Moving very rapidlyaround the nucleus areelectrons. Electronsare much smaller in size andweight than both protons andneutrons. Each electroncarries a negativeelectric charge.
INVESTIGATION 7.4
Modelling an atom AIM To model an atom and observe what makes up most of an atom
METHOD AND RESULTS ◗
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Helium atoms are lighter than all others except hydrogen atoms. This blimp is filled with helium.
Inside the atomIt is now understood that all atoms are made up of small particles.
The amount of negative charge carried by each electron is the same as the amount of positive charge carried by each proton. In an atom, the number of protons is equal to the number of electrons, so there is no overall electric charge.
Atomic numbersThe number of protons in an atom is called its atomic number. Each element has a different atomic number. The blimp above is filled with helium, which has an atomic number of 2. Helium atoms are lighter than all others except hydrogen atoms. All carbon atoms have six protons inside the nucleus, so the atomic number of carbon is 6. For each proton in the carbon atom it also has one electron, meaning a carbon atom has six electrons. Carbon atoms can have 6, 7 or 8 neutrons in their nuclei. The lightest element is hydrogen, which has one proton in each atom and an atomic number of 1. The heaviest natural element is uranium with 92 protons in each atom.
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What’s in a name?As the early scientists discovered more and more elements, it became more important that they all agreed on what to call them. Each element was given a name and a chemical symbol.
The chemical symbols of most elements are very easy to understand. The symbol sometimes starts with the capital letter that is the first letter of the element’s name. For some elements that is the complete symbol. For example:
O = oxygen, C = carbon, N = nitrogen, H = hydrogen.
When there is more than one element starting with the same capital letter, a small letter is also used. For example:
Cl = chlorine, Ca = calcium, Cr = chromium, Cu = copper.
If an element has a symbol that doesn’t match its modern name, that’s because the symbol is taken from the original Greek or Latin name.
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For example:Na = sodium (natrium)Pb = lead (plumbum)Hg = mercury (hydro argyros)Ag = silver (argentum)K = potassium (kalium)Fe = iron (ferrum).
The names and symbols of some of the elements have some interesting origins.• Einsteinium (Es) is named after the famous scientist
Albert Einstein.• Polonium (Po) was discovered by another famous
scientist, Marie Curie. She named polonium after Poland, the country of her birth.
• Helium (He) was first discovered in the sun. It is named after Helios, the Greek god of the sun.
• Sodium (Na) was first called by the Latin name natrium.
• Lead (Pb) also used to have a Latin name, plumbum. That’s where the word ‘plumber’ comes from. The ancient Romans, who spoke Latin, used lead metal to make their water pipes.
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When the atoms of different elements bond together, a compound is formed. When heated together, the elements iron and sulfur form a new compound called iron sulfide. Iron sulfide has the formula FeS. Every compound has a formula comprising the symbols of the elements that make it up. Unlike mixtures, the elements within a compound cannot easily be separated from each other.
Elements can be separated from compounds in several ways. These include:• passing electricity through a compound• burning the compound• mixing the compound with other chemicals.
Each of these methods involves a chemical reaction in which completely different substances are formed.
7.3
Compounding the situationThere are millions and millions of different substances in the world. They include the paper of this book, the ink in the print, the air in the room, the glass in the windows, the wool of your jumper, the cotton and polyester in your shirt or dress, the wood of your desk, the paint on the walls, the plastic of your pen, the hair on your head, the water in the taps and the metal of the chair legs. The list could go on and on.
All substances can be placed into one of three groups: elements, compounds or mixtures.• Elements are substances that contain only one type
of atom. Very few substances exist as elements. Most substances around us are either compounds or mixtures.
• Compounds are usually very different from the elements of which they are made. In compounds, the atoms of one element are bonded very tightly to the atoms of another element or elements. The elements that make up a compound are completely different substances from the compound. For example, pure salt (sodium chloride) is a compound made up of the elements sodium (a silvery metal) and chlorine (a green, poisonous gas).
• Mixtures can be made up of two or more elements, two or more compounds or a combination of elements and compounds. The substances that make up mixtures can usually be easily separated from each other. When the parts of a mixture are separated, no new substances are formed. Fizzy soft drink is a good example of a mixture. It contains water, gas, sugar and flavours. If you shake the soft drink, the gas bubbles separate from the water and go into the air. You still have the water in the bottle and the gas in the air; they are just not mixed together any more. The parts of the mixture can be separated quite easily. The gas escapes when the lid of the container is opened, and the water can be separated by evaporation, leaving behind sugar and some other substances.
Some common substances
Substance Type Composed of: Scientific name
Gold Element Gold Gold
Diamond Element Carbon Carbon
Water Compound Hydrogen and oxygen Dihydrogen oxide
Pure salt Compound Sodium and chlorine Sodium chloride
Brass Mixture Copper and zinc Brass
Soft drink Mixture Water, sugar, carbon dioxide and other compounds
Sea water Mixture Water, sodium chloride and other compounds
A compound is completely different from the elements of which it is made. Pure salt consists of the elements sodium and chlorine. Table salt is a mixture that consists mainly of pure salt.
WHAT DOES IT MEAN?
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Splitting waterWe are surrounded by water. It is in our taps, in our bodies, in the rivers, in the sea, in the air and it comes down as rain. We wash in it, cook with it and drink it. We cannot live without water. Water is not an element — it can be broken down into simpler substances. The illustration below shows an apparatus called a Hofmann voltameter. Water is placed in the voltameter, which is connected to a battery. The electricity splits the water into the elements of which it is made: hydrogen and oxygen.
Hydrogen and oxygen are both elements. They are both gases, and they look the same; they have no colour and no smell. Oxygen is necessary for substances to burn — even hydrogen does not burn without it. Hydrogen is a much less dense gas than oxygen. This means that a balloon filled with hydrogen will float up very high, but one filled with oxygen will not.
The element hydrogen is present in almost all acids. By placing a piece of metal in an acid, the hydrogen is forced out. The hydrogen can be collected and tested with a flame.
The element oxygen is present in water, air, rocks and even hair bleach. Oxygen is the gas that all living things need to stay alive. It is also necessary for all substances to burn. When hydrogen gas is burned, it combines with oxygen in the air to form water. This releases a lot of energy. If large amounts of hydrogen and oxygen are used, enough energy can be released to lift a space rocket.
INVESTIGATION 7.6
Making a compound from its elements AIM To use a chemical reaction to make a compound from its elements
METHOD AND RESULTS ◗
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Crucible
Pipeclay triangle
Tripod
Bunsen burner
Lid
Magnesium ribbon inside
6V batteryor power supply
Hydrogen
Oxygen
Water
Water is split in a Hofmann voltameter. The clear gas in the left tube is hydrogen. The gas in the right tube is oxygen. What do you notice about the amounts of hydrogen and oxygen that are produced?
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INVESTIGATION 7.7
Let’s collect an element AIM To observe a chemical reaction between a metal and an acid
METHOD AND RESULTS ◗
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Dilute hydrochloric acid
Piece of magnesium metal
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7.3 Pure substances and mixtures
worksheet
Collect the hydrogen gas by placing the second test tube over the first.
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7.4
Grouping elementsIt is often convenient to group objects that have features in common. Shops provide a good example of this. In a department store, the goods are grouped so that you know where to buy them. You go to the clothing section for a new pair of jeans, to the jewellery section for a new watch and to the food section for a packet of potato chips.
Scientists also organise objects into groups. Biologists organise living things into groups. Animals with backbones are divided into mammals, birds, reptiles, amphibians and fish. Geologists organise rocks into groups. The elements that make up all substances can also be organised into groups.
Metals and non-metalsScientists have divided the elements into two main groups: the metals and the non-metals.
MetalsThe metals have several features in common:• They are solid at room
temperature, except for mercury, which is a liquid.
• They can be polished to produce a high shine or lustre.
• They are good conductors of electricity and heat.
• They can all be beaten or bent into a variety of shapes. We say they are malleable.
• They can be made into a wire. We say they are ductile.
• They usually melt at high temperatures. Mercury, which melts at –40°C, is one exception.
Non-metalsOnly 22 of the elements are non-metals. At room temperature, 11 of them are gases, 10 are solid and 1 is liquid. The solid non-metals have most of the following features in common:• They cannot be polished to give
a shine like metals; they are usually dull or glassy.
• They are brittle, which means they shatter when they are hit.
• They cannot be bent into shape.• They are usually poor conductors
of electricity and heat.• They usually melt at
low temperatures.
MetalloidsSome of the elements in the non-metal group look like metals. One example is silicon. While it can be polished like a metal, silicon is a poor conductor of heat and electricity, and cannot be bent or made into wire. Those
elements that have features of both metals and non-metals are called metalloids. There are eight metalloids altogether: boron, silicon, arsenic, germanium, antimony, polonium, astatine and tellurium.
Common examples of non-metals are sulfur, carbon and oxygen.
Metalloids are important materials often used in electronic components of computer circuits.
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INVESTIGATION 7.5
Looking for similarities AIM To describe the characteristics of a variety of elements
METHOD AND RESULTS
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ElementShiny or
dull?Does it bend?
Does it conduct electricity?
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VOLTSAC
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Power supply(transformer)
Element tobe tested
Contacts(alligator clips)
Lamp
Connect your element sample into this circuit.
7.2 Metals and non-metalsworksheet
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7.5
Patterns, order and organisation: Chemical name tagsAs more and more elements were being discovered, the early scientists began to find that some of them had things in common.
1Hydrogen
H1.008
2Helium
He4.003
3Lithium
Li6.94
4Beryllium
Be9.02
11Sodium
Na22.99
12Magnesium
Mg24.31
19Potassium
K39.10
20Calcium
Ca40.08
21Scandium
Sc44.96
22Titanium
Ti47.87
23Vanadium
V50.94
24Chromium
Cr52.00
25Manganese
Mn54.94
26IronFe
55.85
27Cobalt
Co58.93
37Rubidium
Rb85.47
38Strontium
Sr87.62
39Yttrium
Y88.91
40Zirconium
Zr91.22
41Niobium
Nb92.91
42Molybdenum
Mo95.96
43Technetium
Tc98.91
44Ruthenium
Ru101.1
45Rhodium
Rh102.91
55Caesium
Cs132.9
56Barium
Ba137.3
57–71Lanthanides
72Hafnium
Hf178.5
73Tantalum
Ta180.9
74Tungsten
W183.8
75Rhenium
Re186.2
76Osmium
Os190.2
77Iridium
Ir192.22
57Lanthanum
La138.91
58Cerium
Ce140.122
59Praseodymium
Pr140.91
60Neodymium
Nd144.24
61Promethium
Pm(145)
62Samarium
Sm150.4
89Actinium
Ac(227)
90Thorium
Th232.04
91Protactinium
Pa231.04
92Uranium
U238.03
93Neptunium
Np237.05
94Plutonium
Pu(244)
87Francium
Fr
88Radium
Ra
89–103Actinides
104Rutherfordium
Rf
105Dubnium
Db
106Seaborgium
Sg
107Bohrium
Bh
108Hassium
Hs
109Meitnerium
Mt
Lanthanides
Transition metals
Actinides
Period 2Period 1
Group 1 Group 2
Group 3 Group 4 Group 5 Group 6 Group 7 Group 8 Group 9Period 3
Period 4
Period 5
Period 6
Period 7
KeyAtomic numberNameSymbolRelative atomic mass
Alkalineearth metals
Alkalimetals
Group 10 Group 11 Group 12
9Fluorine
F19.00
10Neon
Ne20.18
17Chlorine
Cl35.45
18Argon
Ar39.95
7Nitrogen
N14.01
8Oxygen
O16.00
15Phosphorus
P30.97
16Sulfur
S32.06
5Boron
B10.81
6Carbon
C12.01
13Aluminium
Al26.98
14Silicon
Si28.09
28Nickel
Ni58.69
29Copper
Cu63.55
30ZincZn
65.38
31Gallium
Ga69.72
32Germanium
Ge72.63
33Arsenic
As74.92
34Selenium
Se78.96
35Bromine
Br79.90
36Krypton
Kr83.80
46Palladium
Pd106.4
47Silver
Ag107.9
48Cadmium
Cd112.4
49Indium
In114.8
50TinSn
118.7
51Antimony
Sb121.8
52Tellurium
Te127.8
53Iodine
I126.9
54Xenon
Xe131.3
78Platinum
Pt195.1
110Darmstadtium
Ds
111Roentgenium
Rg
79GoldAu
197.0
80Mercury
Hg200.6
81Thallium
Tl204.4
82LeadPb
207.2
83Bismuth
Bi209.0
84Polonium
Po(209)
85Astatine
At(210)
86Radon
Rn(222)
63Europium
Eu151.96
64Gadolinium
Gd157.25
65Terbium
Tb158.93
66Dysprosium
Dy162.50
67Holmium
Ho164.93
68Erbium
Er167.26
69Thulium
Tm168.93
70Ytterbium
Yb173.04
71Lutetium
Lu174.97
95Americium
Am(243)
96Curium
Cm(247)
97Berkelium
Bk(247)
98Californium
Cf(251)
99Einsteinium
Es(254)
100Fermium
Fm(257)
101Mendelevium
Md(258)
102Nobelium
No(255)
103Lawrencium
Lr(256)
Group 13 Group 14 Group 15 Group 16 Group 17 Group 18
Non-metalsMetals
Halogens Noble gases
112Copernicium
Cn
The periodic table. Elements 1–92 all occur naturally. Those from element 93 onwards have been made in laboratories and are all radioactive. Those from element 112 onwards are not shown in this table.
Because some elements had things in common, scientists decided to organise them into groups. It took a long time and a lot of experimenting to work out the groups. A Russian scientist called Dmitri Mendeleev finally worked out a system for grouping the elements. His system is called the periodic table and a modern version is used by scientists today.
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Looking for similaritiesA vertical column on the periodic table is called a group. Elements in the same group on the periodic table always have some features in common. Sometimes these common features are easy to observe, but some of the similarities are not so obvious. For example, neon and argon are gases that do not change when mixed with other elements except under extreme circumstances. They are said to be inert. These two gases are found in the last group of the periodic table along with three other inert gases. The group containing the inert gases is called the noble gas group.
UNDERSTANDING AND INQUIRINGREMEMBER
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1Hydrogen
H1.008
2Helium
He4.003
3Lithium
Li6.94
4Beryllium
Be9.02
11Sodium
Na22.99
12Magnesium
Mg24.31
19Potassium
K39.10
20Calcium
Ca40.08
21Scandium
Sc44.96
22Titanium
Ti47.87
23Vanadium
V50.94
24Chromium
Cr52.00
25Manganese
Mn54.94
26IronFe
55.85
27Cobalt
Co58.93
37Rubidium
Rb85.47
38Strontium
Sr87.62
39Yttrium
Y88.91
40Zirconium
Zr91.22
41Niobium
Nb92.91
42Molybdenum
Mo95.96
43Technetium
Tc98.91
44Ruthenium
Ru101.1
45Rhodium
Rh102.91
55Caesium
Cs132.9
56Barium
Ba137.3
57–71Lanthanides
72Hafnium
Hf178.5
73Tantalum
Ta180.9
74Tungsten
W183.8
75Rhenium
Re186.2
76Osmium
Os190.2
77Iridium
Ir192.22
57Lanthanum
La138.91
58Cerium
Ce140.122
59Praseodymium
Pr140.91
60Neodymium
Nd144.24
61Promethium
Pm(145)
62Samarium
Sm150.4
89Actinium
Ac(227)
90Thorium
Th232.04
91Protactinium
Pa231.04
92Uranium
U238.03
93Neptunium
Np237.05
94Plutonium
Pu(244)
87Francium
Fr
88Radium
Ra
89–103Actinides
104Rutherfordium
Rf
105Dubnium
Db
106Seaborgium
Sg
107Bohrium
Bh
108Hassium
Hs
109Meitnerium
Mt
Lanthanides
Transition metals
Actinides
Period 2Period 1
Group 1 Group 2
Group 3 Group 4 Group 5 Group 6 Group 7 Group 8 Group 9Period 3
Period 4
Period 5
Period 6
Period 7
KeyAtomic numberNameSymbolRelative atomic mass
Alkalineearth metals
Alkalimetals
Group 10 Group 11 Group 12
9Fluorine
F19.00
10Neon
Ne20.18
17Chlorine
Cl35.45
18Argon
Ar39.95
7Nitrogen
N14.01
8Oxygen
O16.00
15Phosphorus
P30.97
16Sulfur
S32.06
5Boron
B10.81
6Carbon
C12.01
13Aluminium
Al26.98
14Silicon
Si28.09
28Nickel
Ni58.69
29Copper
Cu63.55
30ZincZn
65.38
31Gallium
Ga69.72
32Germanium
Ge72.63
33Arsenic
As74.92
34Selenium
Se78.96
35Bromine
Br79.90
36Krypton
Kr83.80
46Palladium
Pd106.4
47Silver
Ag107.9
48Cadmium
Cd112.4
49Indium
In114.8
50TinSn
118.7
51Antimony
Sb121.8
52Tellurium
Te127.8
53Iodine
I126.9
54Xenon
Xe131.3
78Platinum
Pt195.1
110Darmstadtium
Ds
111Roentgenium
Rg
79GoldAu
197.0
80Mercury
Hg200.6
81Thallium
Tl204.4
82Lead
Pb207.2
83Bismuth
Bi209.0
84Polonium
Po(209)
85Astatine
At(210)
86Radon
Rn(222)
63Europium
Eu151.96
64Gadolinium
Gd157.25
65Terbium
Tb158.93
66Dysprosium
Dy162.50
67Holmium
Ho164.93
68Erbium
Er167.26
69Thulium
Tm168.93
70Ytterbium
Yb173.04
71Lutetium
Lu174.97
95Americium
Am(243)
96Curium
Cm(247)
97Berkelium
Bk(247)
98Californium
Cf(251)
99Einsteinium
Es(254)
100Fermium
Fm(257)
101Mendelevium
Md(258)
102Nobelium
No(255)
103Lawrencium
Lr(256)
Group 13 Group 14 Group 15 Group 16 Group 17 Group 18
Non-metalsMetals
Halogens Noble gases
112Copernicium
Cn
The group number corresponds to the number of electrons in the outer shell.
The period number refers to the number of the outermost shell containing electrons.
New radioactive elements are still being produced — the most recent one at the time of publication was element 118.
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7.6
Making moleculesThe naturally occurring elements are the building blocks of everything in our world. The atoms of various elements can be joined in a wide variety of ways to produce many compounds. Elements and compounds can be combined in many ways to make countless mixtures.
Atoms can join, or bond, in many different ways. In some substances, atoms are joined in groups called molecules. For example, in oxygen gas, oxygen atoms are joined in groups of two. In the
compound carbon dioxide, one carbon and two oxygen atoms are joined in every molecule. Atoms can join to form small or large molecules of many different shapes.
Some compounds are not made up of molecules. Instead the atoms bond by lining up one after the other. Sodium bonds to chlorine, which bonds to sodium and so on. Common table salt is an example of a substance that is bonded in this way.
INVESTIGATION 7.8
Mix ’n’ match AIM To model the molecules of a variety of compounds
METHOD AND RESULTS ◗
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DISCUSS AND EXPLAIN
1
2
3
4
2 cm
2 cm
2 cm
2 cm2 cm
2 cm
1.5 cm
A green diamond represents an atom of oxygen. Together, two diamonds represent a molecule of oxygen.
Cut these shapes from coloured paper.
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Compounds of today and tomorrowPolymer is the name given to a compound made of molecules that are long chains of atoms. Most polymers are made up of chains containing carbon atoms. Plastics are synthetic polymers, while cotton and rubber are examples of natural polymers. Although scientists first developed polymers in laboratories in the 1800s, it was not until after World War II that most modern polymers were invented. Modern polymers are used in food wrapping, paint,
WHAT DOES IT MEAN?
HOW ABOUT THAT!
Models representing the molecules of the compounds (a) carbon dioxide, (b) water and (c) methane. The black balls represent carbon; the red, oxygen; and the white, hydrogen.
(a)
(b)
(c)
UNDERSTANDING AND INQUIRINGREMEMBER
1
2
3
4
THINK
5
6
INVESTIGATE
7
8
Compound Formula Number of elements Names of elements
Copper sulfate CuSO4 3 Copper, sulfur, oxygen
Zinc sulfide ZnS
Ammonia NH3
Sulfuric acid H2SO4
Hydrochloric acid HCl
Table salt NaCl
7.4 The periodic table — atomic structure
worksheet
plastic ‘glass’, polystyrene foam for packaging and cups, note money, cases for electronic appliances such as computers and televisions, clothing, glues, shopping bags, sports equipment and even tea bags!
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7.7
Carbon: It’s everywhereThat’s carbon?Carbon is a most amazing element. It is found naturally in three different forms. One form is diamond, another is graphite (the ‘lead’ in lead pencils), and the third is called amorphous carbon (coal, charcoal and soot). Diamond is the hardest substance known and is used to make drill tips and cutting tools. The three forms are different from each other because the carbon atoms are joined in different ways.
Carbon is found combined with other elements in a huge range of compounds. No other element forms as many different types of compounds as carbon. Carbon is found in everything from the skin of an elephant to paint on the walls!
The chemistry of lifeAll living things are made up of compounds including proteins, fats and carbohydrates. The main element in these compounds is carbon. Carbon is not found only in living things, but also in the air in carbon dioxide and under the sea in limestone. The carbon atoms in carbon dioxide were once carbon atoms in living things. The carbon atoms in living things will eventually become carbon atoms in the air or carbon atoms in limestone under the sea. The illustration below shows how nature constantly recycles carbon atoms.
Plants take in carbon dioxide through their leaves and, in a process known as photosynthesis, use the carbon
dioxide and water to make sugar. Sugar is a compound made up of carbon, hydrogen and oxygen atoms. Plants use the sugar to make other substances and for energy to grow. Animals eat plants or plant-eating animals. The carbon atoms then become part of the animals’ bodies.
Carbon atoms in the bodies of living things return to the air in several ways: respiration, decomposition and burning.• Respiration is a process that occurs in the cells of
every living thing, from a microscopic water plant to a humpback whale. Respiration releases energy and produces carbon dioxide. The carbon dioxide released by the cells in your body is taken by your blood to your lungs. The carbon dioxide that you breathe out contains carbon atoms that were once part of your body.
• Decomposition is what happens when plant or animal material breaks down, such as in a compost heap or after something is buried. Microscopic living creatures called decomposers absorb some of the substances in the dead material and release carbon dioxide to the air by respiration.
• When substances containing carbon are burned, carbon dioxide is released. Coal, natural gas and oil are all fuels formed from living things, and contain carbon atoms. Fuels are combustible; that is, they are easily ignited. When these fuels are burned in homes, cars, factories and power stations, carbon dioxide is released into the air. Bushfires also release carbon dioxide back to the air.
Both plantsand animalsrelease CO2. Plants release
oxygen duringthe day.
Plants absorbCO2 duringthe day.
Fossil fuelsrelease CO2when burned.
Petroleum Oil
Gas Coal
Animals absorbcarbon whenthey eat plants.
Plants absorbsome oxygen.
The flow of carbon atoms through the environment
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INVESTIGATION 7.9
Looking for carbon AIM To test for the presence of carbon in a range of substances
METHOD AND RESULTS
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1
DISCUSS AND EXPLAIN
1
2
3
UNDERSTANDING AND INQUIRINGREMEMBER
1
2
3
4
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THINK
6
7
8
9
INVESTIGATE
10
State
Solid Liquid Gas
MaterialCarbon
content (%)Heat production
(MJ)
Wood 11 17.9
Brown coal 73 29.5
Black coal 80 35.9
Natural graphite 90 39
Substance Observations Is carbon present?
Wood
Cotton wool
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ELEMENTS AND ATOMS
■ describe some common chemical elements ■ recall the chemical symbols of some common elements ■ identify some of the dangers associated with some
chemical elements ■ model the structure of the atom and describe the
characteristics of the three main particles ■ recall that each chemical element is identified with
a unique atomic number, which is equal to the number of protons in its nucleus
■ distinguish between metals, non-metals and metalloids ■ identify similar properties of groups of elements in the
periodic table
COMPOUNDS AND MIXTURES
■ distinguish between elements, compounds and mixtures ■ recall that the atoms in compounds are bonded very
tightly together ■ recall that elements can be separated from compounds
only through a chemical reaction
■ recognise that the properties of compounds are different from the elements that make them up
■ use the formulas of simple compounds to identify the elements that make them up
■ model the arrangement of atoms in the molecules of some compounds
■ identify and describe some common compounds and their uses
SCIENCE AS A HUMAN ENDEAVOUR
■ describe how the understanding of the particles that make up all matter has changed over time
■ explain how the ideas about elements and the atom have changed over time
■ describe the contributions of some of the scientists who have added to our knowledge of the atom and the elements
■ recognise the impact of new scientific discoveries and technology on our understanding of the atom, elements and compounds
STUDY CHECKLIST
DIGITAL RESOURCES
FOCUS activity Access more details about focus activities for this chapter in your eBookPLUS.
doc-10560
Interactivities
It’s elementary! revelation gameIn this revelation game, you must identify common elements from their symbols to reveal the full periodic table. You must answer quickly to complete the game in time.
Searchlight ID: int-0229
Making moleculesIn this interactivity, you will use carbon, chlorine, hydrogen, nitrogen and oxygen atoms to create the correct models of a series of chemical formulae. Instant feedback is provided.
Searchlight ID: int-0228
Add ‘Lavoisier and hydrogen’ watch a video from The story of science about the discovery of the elements.Searchlight ID: eles-1722
AnSwerS for this chapter can be found online in your eBookPLUS.
Online sectionThis section of the chapter can be found online in your eBookPLUS.
7.8 Thinking tools: Affinity diagrams and cluster maps
Individual pathways
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LOOKING BACK
(b) To which group in the periodic table does this element belong?
13 What event must take place in order to separate a compound into separate elements?
14 How are the molecules in polymers different from the molecules of other compounds?
15 Complete the table on the next page to indicate whether the substances listed are elements, compounds or mixtures. Also indicate why you made that decision.
10 Complete the following table to summarise what you know about metals and non-metals.
Metals non-metals
Conduct electricity well
Conduct heat well
Surface features
State at room temperature
Malleable
Ductile
Brittle
11 Which of the elements iron, lead, hydrogen, oxygen, silicon, uranium and sodium are:(a) metals(b) metalloids(c) non-metals?
12 (a) Which element is used inside illuminated signs like the one below?
++
Link to assessON for questions to test your readiness FOr learning, your progress AS you learn and your levels OF achievement. www.assesson.com.au
1 About 2500 years ago, Democritus suggested what all substances were made up of.(a) In what way was Democritus’ idea about substances
the same as the model that scientists currently use to describe substances?
(b) Suggest why most thinkers of the time disagreed with Democritus.
2 Copy and complete the following table, which describes the structure of atoms.
Part of atom Location
Size and weight
(relative)electric charge
Large Positive
Neutron
Outside the nucleus
3 If a neutral atom has 12 protons, how many electrons does it have?
4 What takes up most of the space in an atom?5 Identify the one feature that every single atom of the
element sodium has in common.6 What is the atomic number of each of the
following elements?(a) Hydrogen(b) Carbon(c) Uranium
7 How many protons does each of the elements listed in question 6 have in its nucleus?
8 How many electrons does each of the elements listed in question 6 have in its nucleus?
9 Make a copy of the diagram of the atom below and label an electron and the nucleus. Answer the following questions.(a) How many protons does this atom have?(b) How many neutrons does this atom have?(c) How many electrons does this atom have?(d) What is the atomic number of this atom?(e) Describe one use of the element that is made up of
these atoms.
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Substance
element, compound or
mixturewhy do you
think so?
Gold
Diamond
Carbon dioxide
Air
Sea water
Pure water
Iron
Ammonia
Table salt (NaCl)
16 Which of ‘the bits that matter’ is represented by each of the cartoons below?
18 Each of the diagrams below represents one of ‘the bits that matter’ that make up substances.
17 What do diamonds, the ‘lead’ in pencils and coal have in common?
A B
C D
E F
G H
I J
K L
19 Which of the diagrams represents:(a) an atom of an element(b) a molecule of an element(c) a molecule of a compound?
20 Most of the substances around you are compounds and mixtures.(a) What differences could be observed between a mixture
of hydrogen and oxygen, and a compound of hydrogen and oxygen?
(b) Explain the difference between a compound and a mixture in your own words.
21 Respiration is a chemical reaction in which carbon dioxide is produced.(a) Where in your body does respiration take place?(b) What is released during respiration apart from
carbon dioxide?(c) Suggest how the carbon atoms in carbon dioxide enter
your body.22 Why doesn’t water appear in the periodic table?
7.5 Summing upworksheet
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ICT ACTIvITY
Science TVSEARCHLIGHT ID: PRO-0090
ScenarioIn the media world, programs that combine entertainment and education are known as ‘edutainment’. With the success of edutainment programs such as Mythbusters (SBS/7Mate), Scope (Network 10) and The ExperiMentals (ABC), it seems that science is attracting a bigger share of the television market than many network executives would have expected. Now, your local TV network — Channel 55 — has decided to jump on the ‘science as edutainment’ bandwagon and has announced that next year it will develop a program called Science TV. To make Science TV more appealing to a younger audience, the developing executives of the program want it to be presented by a team of school students, who will do all of the introductions, explanations and experiments for each of the segments. It is important that the right team of students is found or the program will be canned after only a few episodes, so Channel 55 has announced that it is accepting online audition files from groups of students who think they have what it takes to be the Science TV stars.
Your taskYour group is going to put together a video submission that you could send to the Channel 55 developers to showcase how suitable you would be as the stars of Science TV.
The guidelines for the video submission from the Channel 55 website are as follows:• The video must be between four and five minutes in length.• The target audience of Science TV is between 8 and
14 years old.• At least two people must be shown on camera.• The video must be in the form of a chemistry segment that
explains one of the following:a. What is the difference between a physical change and
a chemical change?b. What are elements, compounds and mixtures?c. How would we separate a mixture of iron filings, sand,
copper sulfate and chalk dust?• At least one experiment must be shown being performed
in the segment — the experiment must be relevant to the segment and safe to perform (i.e. no explosions and no dangerous fumes produced).
The segment should be engaging and informative. It should have an introduction (either a scenario played out or a discussion between the presenters), an experiment to either test or demonstrate an idea, an explanation of the main concepts involved and a resolution that ties back into the original scenario or discussion. Remember: the main idea is to show that science is FUN!
ProcessOpen the ProjectsPLUS application for this chapter located in your eBookPLUS. Watch the introductory video lesson and then click the ‘Start Project’ button to set up your project group. Save your settings and the project will be launched. The rest of the process is outlined online in your ProjectsPLUS application.
